[Haskell-cafe] Re: Improving MTL instances (was: Overlapping/Incoherent instances)

Don Stewart dons at galois.com
Mon Oct 13 03:35:04 EDT 2008

> On Mon, Oct 13, 2008 at 2:04 AM, J. Garrett Morris
> <jgmorris at cecs.pdx.edu> wrote:
> > Indeed - MTL seems to have been rewritten at some point in the past to
> > prefer exhaustive enumeration to overlap.
> Indeed, and I actually think this is a weakness of the current
> implementation.  Anyone who comes up with a new transformer that
> provides different functionality than what is there needs to
> explicitly provide all the relevant instances, instead of letting
> MonadTrans do its thing.

I just want to make one small point here encouraging people to try out
new 'mtl' libraries. There are lots of *new* monad libraries,

The new & improved mtl:

    * monadLib http://hackage.haskell.org/cgi-bin/hackage-scripts/package/monadLib

As well as,

    * mmtl http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mmtl
    * mtl-tf http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mtl-tf
and the huge,

    * category-extras http://hackage.haskell.org/cgi-bin/hackage-scripts/package/category-extras

'mtl' isn't magic in any way. it isn't distributed with ghc, so we can
let the (library) free market pick a winner.

Now, if the monadLib guys would advertise their work a bit more

-- Don

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